The present invention relates to the art of magnetic resonance imaging. It finds particular application in conjunction with Magnetic Resonance Angiography (MRA) and will be described with particular reference thereto. However, it should be appreciated that the present invention may also find application in conjunction with magnetic resonance spectroscopy, and other medical and diagnostic techniques, and the like.
Maximum Intensity Processing (MIP) is a common and powerful tool in clinical angiograms in connection with computer tomography (CT) and magnetic resonance imaging (MRI). Projection images are especially useful for screening vascular morphology and pathological diseases, such as stenosis, atherosclerosis and aneurysm. In clinical diagnosis, radiologists preferably view projection images rather than MRI slice images.
A MIP image is essentially a projection of a three-dimensional (3D) volume from a designated viewing point. The brightest pixel along each specified path from the view is picked to form the projection image. MIP images can be acquired from different viewing points, providing radiologists with flexibility to study cases. In MIP processing, the user also defines an area of interest. The tissues outside this area are excluded in the MIP process and therefore do not contribute to the finally formed MIP images. This improves the quality of the projection images. Because all the imaging data is always available, the user may also change the definition of the area of interest, if desired.
Currently, on most of the conventional MRI scanners, MRA MIP images are created after all axial (original) images are acquired. That is, only after the whole imaging process is completely accomplished, can the MIP process be initiated.
Commonly, the scanning process and MIP process are performed sequentially. It takes approximately 7-15 minutes to acquire image data during the initial data acquisition or scanning step. The MIP processing is performed after all of the image data has been acquired. Thus, from the start of scanning, approximately 15-20 minutes elapse before a radiologist can view the MRA MIP images and render a diagnosis. If the resulting MIP images are not of sufficient quality to permit a diagnosis due to, e.g. improper scanning parameters or incorrect volume coverage etc., an additional 15-20 minutes must be expended in order to repeat the process.
Most MRI vendors provide a feature for MRA, which displays the acquired axial (original) images while scanning is still being performed. This provides some information but is rather limited since MIP images are different than axial images, and there is no explicit information to indicate the relative position of axial images relative to the MIP images. Further, in the case where poor quality images, incorrect positioning or unnecessary images (slices) are generated, the data acquisition step can not be interrupted in order to start a new imaging step. Thus, the only option available is to complete the present data acquisition phase and then repeat the entire scan procedure with modified parameters.
In most cases, radiologists can not determine the exact volume coverage to be imaged before hand. Thus, an oversampling strategy is usually used to collect more slices which slices may not be necessary for the diagnosis. Collection of additional and/or unnecessary slices prolongs the imaging time, and results in decreased clinical diagnostic throughput.
The present invention contemplates a new and improved Magnetic Resonance Angiography (MRA) screening technique which overcomes the above-referenced problems and others.